1. Field of the Invention
The present invention relates to an endoscope system, a processor device for an endoscope system, an operation method for an endoscope system, and an operation method for a processor device for calculating biological function information regarding the oxygen saturation of blood hemoglobin from an image signal obtained by imaging an observation target in a subject.
2. Description of the Related Art
In the medical field, it is common to perform diagnosis using an endoscope system including a light source device, an endoscope, and a processor device. In recent years, diagnosis of a lesion using the oxygen saturation of blood hemoglobin, among the pieces of biological function information, has been performed. In particular, it is possible to determine the normal tissue and the cancer tissue based on the oxygen saturation (JP2012-213550A and JP2012-125402A). In JP2012-213550A, the distributions of the oxygen saturation of the surface layer, the intermediate layer, and the deep layer of the observation target are displayed by changing the combination of emitted light, so that it is possible to determine the state of the cancer tissue in more detail.
As a method of acquiring the oxygen saturation, a method is known in which first signal light and second signal light having different wavelength bands and different absorption coefficients for oxygenated hemoglobin and reduced hemoglobin alternately irradiate blood vessels in the mucous membrane and the reflected light beams of the first and the second signal light beams are detected by a sensor located at the distal portion of the endoscope (refer to JP2012-213550A and JP2012-125402A).
A ratio between a first signal light image signal corresponding to the reflected light of the first signal light detected by the sensor and a second signal light image signal corresponding to the reflected light of the second signal light detected by the sensor (hereinafter, referred to as a signal ratio) is maintained at a fixed value in a case where there is no change in oxygen saturation in blood vessels. However, in a case where a change in oxygen saturation occurs, the signal ratio changes with the oxygen saturation change. Accordingly, it is possible to calculate the oxygen saturation based on the signal ratio between the first signal light image signal and the second signal light image signal.